This invention pertains to hermetic rotary compressors for compressing refrigerant in refrigeration systems such as refrigerators, freezers, air conditioners and the like. In particular, this invention relates to reducing frictional loading of the crankshaft and eccentric.
In general, prior art rotary hermetic compressors comprise a housing in which are disposed a motor and compressor cylinder block. The motor drives a crankshaft for revolving a rotor or roller (piston) inside the cylinder. One or more vanes are slidably received in slots located through the cylinder walls for separating areas at suction and discharge pressure within the cylinder bore. The vanes, cooperating with the rotor and cylinder wall, provide the structure for compressing refrigerant within the cylinder bore.
The operating parts of rotary hermetic compressors are machined to extremely close tolerances and the surfaces of the parts are finished to a high degree in order to prevent leakage and thereby provide a very efficient compressor. Preventing leakage of refrigerant from high pressure areas to low pressure areas is of main concern to increasing compressor efficiency.
One of the problems encountered in prior art hermetic compressor arrangements has been high frictional loading between the vane tip and the rolling piston, and between the piston and the cylinder wall. The vane necessarily has to be highly loaded against the piston to prevent compressed refrigerant leakage. At times, insufficient oil reaches the critical wear areas of the vane tip and piston, thereby increasing the wear rate of each. A reduction in the frictional loading on the vane tip would reduce wear and increase compressor efficiency. Additional sources of wear and friction are at the interface of the outboard or inboard bearings and the eccentric within the cylinder block.
U.S. Pat. No. 3,343,782 discloses a rotor having washer like elements secured to each end of the rotor by endplates. These washer like elements are flexible carbon washers which provide bearing surfaces between the endwalls of the rotor and housing. A problem with this structure is that it requires grinding the faces of the washers to eliminate burrs. Further, the washer elements do not assist in oil migration between the rotor and housing endwalls thereby possibly increasing the noise of the compressor.
U.S. Pat. No. 2,864,552 shows a bearing plate for a shaft having a multi-start spiral groove extending across the central portion of the plate. This groove is used to maintain a charge of air pressure to the bearings but is not used specifically for transfer of oil to sliding surfaces. A potential problem with this end plate is that its shape does not control endplay of the shaft.
An additional problem encountered with vertical shaft rotary compressors is an inherent axial crankshaft load caused by the vertical orientation of the crankshaft. Misalignment of the axial position of the rotor relative to the stator is a major source of eccentric side journal loading. The stator, when energized, attempts to center the rotor in the stator iron. Depending on the rotor position, this net force may be upward or downward. This load causes increased friction between portions of the crankshaft and bearings that slide together, specifically the eccentric side journals of the crankshaft eccentric that slide against the cylinder block endwalls. This increased frictional wear reduces the efficiency of the compressor.